U.S. patent number 6,714,370 [Application Number 10/245,189] was granted by the patent office on 2004-03-30 for write head and method for recording information on a data storage medium.
This patent grant is currently assigned to Seagate Technology LLC. Invention is credited to Terry W. McDaniel, Thierry R. Valet.
United States Patent |
6,714,370 |
McDaniel , et al. |
March 30, 2004 |
Write head and method for recording information on a data storage
medium
Abstract
A recording head for use in conjunction with a magnetic storage
medium, comprises a waveguide for providing a path for transmitting
radiant energy, a near-field coupling structure positioned in the
waveguide and including a plurality of arms, each having a planar
section and a bent section, wherein the planar sections are
substantially parallel to a surface of the magnetic storage medium,
and the bent sections extend toward the magnetic storage medium and
are separated to form a gap adjacent to an air bearing surface, and
applying a magnetic write field to sections of the magnetic
recording medium heated by the radiant energy. A disc drive
including the recording head and a method of recording data using
the recording head are also provided.
Inventors: |
McDaniel; Terry W. (Volcano,
CA), Valet; Thierry R. (Sunnyvale, CA) |
Assignee: |
Seagate Technology LLC (Scotts
Valley, CA)
|
Family
ID: |
23359358 |
Appl.
No.: |
10/245,189 |
Filed: |
September 17, 2002 |
Current U.S.
Class: |
360/59;
369/112.09; 369/112.21; 369/112.14; 369/112.27; 369/13.3;
369/13.02; G9B/5.044; G9B/5.04; G9B/5.024; G9B/5.026 |
Current CPC
Class: |
G11B
5/012 (20130101); G11B 5/02 (20130101); G11B
5/127 (20130101); G11B 5/1278 (20130101); G11B
5/314 (20130101); G11B 5/09 (20130101); G11B
5/6088 (20130101); G11B 2005/0005 (20130101); G11B
2005/0021 (20130101); G11B 2005/0029 (20130101); G11B
2005/0002 (20130101) |
Current International
Class: |
G11B
5/127 (20060101); G11B 5/012 (20060101); G11B
5/02 (20060101); G11B 5/00 (20060101); G11B
5/09 (20060101); G11B 005/02 () |
Field of
Search: |
;360/284.5,126,59
;369/121,112-113,13.33,13.02 ;398/1 ;385/33 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1039458 |
|
Sep 2000 |
|
EP |
|
1148370 |
|
Oct 2001 |
|
EP |
|
2001028109 |
|
Jan 2001 |
|
JP |
|
Other References
J Cha et al., "Near-field Optical Data Storage Using a Nanometric
Aperture Array." Journal of the Korean Physical Society, vol. 37,
No. 5, Nov. 2000, pp. 735-738..
|
Primary Examiner: Sniezek; Andrew L.
Assistant Examiner: Colon; Rocio
Attorney, Agent or Firm: Lenart, Esq.; Robert P.
Pietragallo, Bosick & Gordon
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. Provisional Application
No. 60/346,432, filed Jan. 7, 2002.
Claims
What is claimed is:
1. A recording head for use in conjunction with a magnetic storage
medium, comprising: a waveguide for providing a path for
transmitting radiant energy; a near-field coupling structure
positioned in the waveguide and including a plurality of arms, each
having a planar section and a bent section, wherein the planar
sections are substantially parallel to a surface of the magnetic
storage medium, and the bent sections extend toward the magnetic
storage medium and are separated to form a gap adjacent to an air
bearing surface; and means for applying a magnetic write field to
sections of the magnetic recording medium heated by the radiant
energy.
2. The recording head of claim 1, further comprising: a
semi-reflective layer positioned in the path to form a resonant
optical cavity with a surface of the magnetic storage medium.
3. The recording head of claim 2, wherein the semi-reflective layer
is positioned from the magnetic storage medium by a distance
substantially equal to an integer times a half wavelength of the
radiant energy.
4. The recording head of claim 1, wherein the means for applying a
magnetic write field to the magnetic recording medium comprises: a
magnetic yoke having a write pole, a return pole, and a coil for
producing magnetic flux in the yoke, wherein the near-field
coupling structure is position adjacent to the write pole.
5. The recording head of claim 4, wherein the waveguide comprises a
transparent layer mounted adjacent to the write pole.
6. The recording head of claim 4, wherein the write pole is located
down track from the near-field coupling structure.
7. The recording head of claim 1, wherein the plurality of arms
comprises four arms and wherein the bent sections of the arms form
a square opening adjacent to the air bearing surface.
8. The recording head of claim 1, wherein the length of the
near-field coupling structure is substantially equal to an integer
multiple of half or full wavelengths of the radiant in the
waveguide.
9. A magnetic disc drive storage system, comprising: a housing;
means for supporting a magnetic storage medium positioned in the
housing; and means for positioning a recording head adjacent to the
rotatable magnetic storage medium, the recording head including: a
waveguide for providing a path for transmitting radiant energy; a
near-field coupling structure positioned in the waveguide and
including a plurality of arms, each having a planar section and a
bent section, wherein the planar sections are substantially
parallel to a surface of the magnetic storage medium, and the bent
sections extend toward the magnetic storage medium and are
separated to form a gap adjacent to an air bearing surface; and
means for applying a magnetic write field to sections of the
magnetic recording medium heated by the radiant energy.
10. The magnetic disc drive storage system of claim 9, wherein the
recording head further comprises: a semi-reflective layer
positioned in the path to form a resonant cavity with a surface of
the magnetic storage medium.
11. The magnetic disc drive storage system of claim 10, wherein the
semi-reflective layer positioned from the magnetic storage medium
by a distance substantially equal to an integer times a half
wavelength of the radiant energy.
12. The magnetic disc drive storage system of claim 9, wherein the
means for applying a magnetic write field to the magnetic recording
medium comprises: a magnetic yoke having a write pole, a return
pole, and a coil for producing magnetic flux in the yoke, wherein
the near-field coupling structure is position adjacent to the write
pole.
13. The magnetic disc drive storage system of claim 12, wherein the
waveguide comprises a transparent layer mounted adjacent to the
write pole.
14. The magnetic disc drive storage system of claim 12, wherein the
write pole is located down track from the near-field coupling
structure.
15. The magnetic disc drive storage system of claim 9, wherein the
plurality of arms comprises four arms and wherein the bent sections
of the arms form a square opening adjacent to the air bearing
surface.
16. The magnetic disc drive storage system of claim 9, wherein the
means for applying a magnetic field comprises: a perpendicular
write head.
17. The magnetic disc drive storage system of claim 9, wherein the
length of the near-field coupling structure is substantially equal
to an integer multiple of half or full wavelengths of the radiant
energy in the waveguide.
18. A method of recording data on a magnetic storage medium,
comprising: heating a section of the data storage medium by
applying radiant energy to a waveguide including a transparent
layer, a semi-reflective layer, and a near-field coupling structure
at a frequency such that radiant energy resonates between the
semi-reflective layer and a surface of the data storage medium; and
applying a magnetic write field to the section of data storage
medium heated by the radiant energy.
19. A method of recording data according to claim 18, wherein the
near-field coupling structure is spaced apart from a surface of the
data storage medium by a distance of about 2 nm to about 50 nm.
20. A method of recording data according to claim 18, wherein the
semi-reflective layer positioned from the magnetic storage medium
by a distance substantially equal to an integer times a half
wavelength of the radiant energy.
Description
FIELD OF THE INVENTION
This invention relates to the field of data storage, and more
particularly to write heads and methods for recording information
on data storage media using near-field optical coupling
structures.
BACKGROUND OF THE INVENTION
Magnetic recording heads are used in magnetic disc drive storage
systems. Most magnetic recording heads used in such systems today
are "longitudinal" magnetic recording heads. Longitudinal magnetic
recording in its conventional form has been projected to suffer
from superparamagnetic instabilities at densities above
approximately 40 Gbit/in.sup.2. It is believed that reducing or
changing the bit cell aspect ratio will extend this limit up to
approximately 100 Gbit/in.sup.2. However, for recording densities
above 100 Gbit/in.sup.2, different approaches will likely be
necessary to overcome the limitations of longitudinal magnetic
recording.
An alternative to longitudinal recording that overcomes at least
some of the problems associated with the superparamagnetic effect
is "perpendicular" magnetic recording. Perpendicular magnetic
recording is believed to have the capability of extending recording
densities well beyond the limits of longitudinal magnetic
recording. Perpendicular magnetic recording heads for use with
perpendicular magnetic storage media may include a pair of
magnetically coupled poles, including a write pole having a
relatively small bottom surface area and a return pole having a
larger bottom surface area. A coil having a plurality of turns is
located adjacent to the write pole for inducing a magnetic field
between the pole and a soft underlayer of the storage media. The
soft underlayer is located below a hard magnetic recording layer of
the storage media and enhances the amplitude of the field produced
by the write pole. In the recording process, an electric current in
the coil energizes the write pole, which produces a magnetic field.
The image of this field is produced in the soft underlayer to
enhance the field strength produced in the magnetic media. Magnetic
flux that emerges from the write pole passes into the soft
underlayer and returns through the return flux pole. The return
pole is located sufficiently far apart from the main write pole
such that the material of the return pole does not affect the
magnetic flux of the write pole, which is directed vertically into
the hard layer of the storage media. This allows the use of storage
media with higher coercive force, consequently, more stable bits
can be stored in the media.
As the magnetic media grain size is reduced for high areal density
recording, superparamagnetic instabilities become an issue. The
superparamagnetic effect is most evident when the grain volume V is
sufficiently small that the inequality K.sub.U V/k.sub.B T >40
can no longer be maintained. K.sub.u is the material's magnetic
crystalline anisotropy energy density, k.sub.B is Boltzmann's
constant, and T is absolute temperature. When this inequality is
not satisfied, thermal energy demagnetizes the individual grains
and the stored data bits will not be stable. Therefore, as the
grain size is decreased in order to increase the areal density, a
threshold is reached for a given material K.sub.u and temperature T
such that stable data storage is no longer feasible.
The thermal stability can be improved by employing a recording
medium formed of a material with a very high K.sub.u. However, the
available recording heads are not able to provide a sufficient or
high enough magnetic writing field to write on such a medium. Heat
assisted magnetic recording, sometimes referred to as optical or
thermal assisted recording, has been proposed to overcome at least
some of the problems associated with the superparamagnetic effect.
Heat assisted magnetic recording generally refers to the concept of
locally heating a recording medium to reduce the coercivity of the
recording medium so that an applied magnetic writing field can more
easily direct the magnetization of the recording medium during the
temporary magnetic softening of the recording medium caused by the
heat source.
By heating the medium, the K.sub.u or the coercivity is reduced
such that the magnetic write field is sufficient to write to the
medium. Once the medium cools to ambient temperature, the medium
has a sufficiently high value of coercivity to assure thermal
stability of the recorded information. When applying a heat or
light source to the medium, it is desirable to confine the heat or
light to the track where writing is taking place and to generate
the write field in close proximity to where the medium is heated to
accomplish high areal density recording. The separation between the
heated spot and the write field spot should be minimal or as small
as possible so that writing may occur while the medium temperature
is substantially above ambient temperature. This also provides for
the efficient cooling of the medium once the writing is
completed.
In order to increase areal density in an optically assisted write
head, the spot size of the optical beam can be decreased by either
decreasing the wavelength of the light or increasing the numerical
aperture of the focusing elements. Other optical techniques which
either directly or indirectly reduce the effective optical spot
size are generally referred to as "superresolution" techniques. For
example, it is well known that the resolving power of a microscope
can be increased by placing an aperture with a pinhole (having a
diameter smaller than the focused spot size) sufficiently close to
the object being observed. As another example, tapered optical
fibers have been used to achieve superresolution in near field
scanning optical microscopy.
There is identified a need for an improved magnetic recording head
that overcomes limitations, disadvantages, and/or shortcomings of
known optically assisted magnetic recording heads.
SUMMARY OF THE INVENTION
This invention provides a recording head for use in conjunction
with a magnetic storage medium, comprising a waveguide for
providing a path for transmitting radiant energy; a near-field
coupling structure positioned in the waveguide and including a
plurality of arms, each having a planar section and a bent section,
wherein the planar sections are substantially parallel to a surface
of the magnetic storage medium, and the bent sections extend toward
the magnetic storage medium and are separated to form a gap
adjacent to an air bearing surface; and means for applying a
magnetic write field to sections of the magnetic recording medium
heated by the radiant energy.
The recording head can further comprise a semi-reflective layer
positioned in the path to form a resonant cavity with a surface of
the magnetic storage medium. The means for applying a magnetic
write field to the magnetic recording medium can comprise a
magnetic yoke having a write pole, a return pole, and a coil for
producing magnetic flux in the yoke, wherein the near-field
coupling structure is position adjacent to the write pole.
The waveguide can comprise a transparent layer mounted adjacent to
the write pole, wherein the write pole is located down track from
the near-field coupling structure. The near-field coupling
structure can form a square opening adjacent to the air bearing
surface of the recording head.
The invention also encompasses a magnetic disc drive storage system
comprising a housing; means for supporting a magnetic storage
medium positioned in the housing; and means for positioning a
recording head adjacent to the rotatable magnetic storage medium,
wherein the recording head includes a waveguide for providing a
path for transmitting radiant energy; a near-field coupling
structure positioned in the waveguide and including a plurality of
arms, each having a planar section and a bent section, wherein the
planar sections are substantially parallel to a surface of the
magnetic storage medium, and the bent sections extend toward the
magnetic storage medium and are separated to form a gap adjacent to
an air bearing surface; and means for applying a magnetic write
field to sections of the magnetic recording medium heated by the
radiant energy.
The invention further encompasses a method of recording data on a
data storage medium, comprising heating a section of the data
storage medium by applying radiant energy to a waveguide including
a transparent layer, a semi-reflective layer, and a near-field
coupling structure at a frequency such that radiant energy
resonates between the semi-reflective layer and a surface of the
data storage medium; and applying a magnetic write field to the
section of data storage medium.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a pictorial representation of a disc drive that can
include a recording head constructed in accordance with this
invention;
FIG. 2 is a side view of a recording head constructed in accordance
with the invention;
FIG. 3 is a cross-sectional view of a portion of the waveguide of
the recording head of FIG. 2;
FIG. 4 is a cross-sectional view of the portion of the waveguide of
FIG. 3 taken in a plane perpendicular to the view shown in FIG.
3;
FIG. 5 is an isometric view of the near-filed coupling structure of
the recording head of FIG. 2;
FIG. 6 is a side view of an alternative recording head constructed
in accordance with the invention; and
FIG. 7 is a cross-sectional view of a portion of the waveguide of
the recording head of FIG. 6.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the drawings, FIG. 1 is a pictorial representation of
a disc drive 10 that can use a recording head constructed in
accordance with this invention. The disc drive 10 includes a
housing 12 (with the upper portion removed and the lower portion
visible in this view) sized and configured to contain the various
components of the disc drive. The disc drive 10 includes a spindle
motor 14 for rotating at least one magnetic storage medium 16. At
least one arm 18 is contained within the housing 12, with the arm
18 having a first end 20 for supporting a recording head or slider
22, and a second end 24 pivotally mounted on a shaft by a bearing
26. An actuator motor 28 is located at the arm's second end 24 for
pivoting the arm 18 to position the recording head 22 over a
desired sector or track of the disc 16. The actuator motor 28 is
controlled by a controller, which is not shown in this view and is
well known in the art.
FIG. 2 is a partially schematic side view of a perpendicular
magnetic recording head 30 constructed in accordance with the
invention. The recording head includes a magnetic write head 32
that is constructed using known technology and includes a yoke 34
that forms a write pole 36 and a return pole 38. The recording head
30 is positioned adjacent to a perpendicular magnetic storage
medium 40 having a magnetically hard layer 42 and a magnetically
soft layer 44 supported by a substrate 46. An air bearing 48
separates the recording head from the storage medium by a distance
D. A coil 50 is used to control the magnetization of the yoke to
produce a write field at an end 52 of the write pole adjacent to an
air bearing surface 54 of the write head. The recording head 30 can
also include a read head, not shown, which may be any conventional
type read head as is generally known in the art.
The perpendicular magnetic storage medium 40 is positioned adjacent
to or under the recording head 30 and travels in the direction of
arrow A. The recording medium 40 includes a substrate 46, which may
be made of any suitable material such as ceramic glass or amorphous
glass. A soft magnetic underlayer 44 is deposited on the substrate
46. The soft magnetic underlayer 44 may be made of any suitable
material such as, for example, alloys or multilayers having Co, Fe,
Ni, Pd, Pt or Ru. A hard magnetic recording layer 42 is deposited
on the soft underlayer 44, with the perpendicular oriented magnetic
domains 56 contained in the hard layer 42. Suitable hard magnetic
materials for the hard magnetic recording layer 42 may include at
least one material selected from, for example, FePt or CoCrPt
alloys having a relatively high anisotropy at ambient
temperature.
The recording head 30 also includes means for heating the magnetic
storage medium 40 proximate to where the write pole 36 applies the
magnetic write field H to the storage medium 40. Specifically, the
means for heating includes an optical waveguide 58 formed by a
transparent layer 60. The optical waveguide 58 acts in association
with a source 62 of radiant energy which transmits radiant energy
via an optical fiber 64 that is in optical communication with the
optical waveguide 60. The radiant energy can be, for example,
visible light, infrared or ultra violet radiation. The source
provides for the generation of surface plasmons or guided modes
that travel through the optical waveguide 58 toward a heat emission
surface 66 that is formed along the air-bearing surface thereof.
The transmitted radiant energy, generally designated by reference
number 68, passes from the heat emission surface 66 of the optical
waveguide 58 to the surface of the storage medium for heating a
localized area of the storage medium 40, and particularly for
heating a localized area of the hard magnetic layer 42.
The source 62 may be, for example, a laser diode, or other suitable
laser light source. At the surface of the medium 40, the surface
plasmons convert a portion of their energy into heat in the medium
40. The transparent layer may be formed, for example, from a silica
based material, such as SiO.sub.2. The transparent layer should be
a non-conductive dielectric, and have extremely low optical
absorption (high transmissivity). It will be appreciated that in
addition to the transparent layer, the waveguide 58 may include an
optional cladding layer, such as aluminum, positioned adjacent the
transparent layer or an optional overcoat layer, such as an alumina
oxide, for protecting the waveguide 58.
In addition, the waveguide 58 includes a near-field coupling
structure 70 for confining the radiant energy to the recording
spot. Specifically as shown in FIGS. 3, 4 and 5, the near-field
coupling structure includes a plurality of arms 72, 74, 76 and
78.
FIG. 3 is an enlarged cross-sectional view of a portion of the
optical waveguide 58. The waveguide includes a transparent layer 60
and first and second arms 72 and 74, which in this embodiment are
embedded within the transparent layer 60. Arm 72 includes a first
section 80 that is positioned substantially parallel the surface of
the storage medium, and a second section 82 that extends from the
first section toward the air bearing surface at a first angle
.theta..sub.1. Arm 74 includes a first section 84 that is
positioned substantially parallel the surface of the storage
medium, and a second section 86 that extends from the first section
toward the air bearing surface at a second angle .theta..sub.2. The
ends 88 and 90 of the second sections of arms 72 and 74 are
separated to form a gap 92. The gap has a width that can be, for
example, less than 50 nm. The width of the gap determines the
breadth of the near radiation field, and the resulting thermal
field in the medium is desired to be no larger than 50 nm in the
largest dimension.
FIG. 4 is an enlarged cross-sectional view of the portion of the
optical waveguide 58 of FIG. 3 taken in a plane perpendicular to
the plane of FIG. 3. The waveguide is shown to further include
third and fourth arms 76 and 78, which are also embedded within the
transparent layer. Arm 76 includes a first section 94 that is
positioned substantially parallel the surface of the storage
medium, and a second section 96 that extends from the first section
toward the air bearing surface at a first angle .theta..sub.3. Arm
78 includes a first section 98 that is positioned substantially
parallel the surface of the storage medium, and a second section
100 that extends from the first section toward the air bearing
surface at a second angle .theta..sub.4. The ends 102 and 104 of
the second sections of arms 76 and 78 are separated to form a gap
106.
FIG. 5 is an isometric view of the arms 72, 74, 76 and 78, which
are positioned together to form the near-field coupling structure
70. In this view, the bent sections of the arms are seen to have a
trapezoidal shape. The ends of the arms form an opening 110 for
passage of radiant energy from the light source. While the opening
is illustrated as having a square shape, it will be appreciated
that other shapes can be used. The arms should be made of excellent
conductors in the optical frequency band, such as Au, Ag or Cu. The
overall length of the arms, designated as L in FIGS. 3 and 4, can
be determined by a resonant condition with the exciting radiation
in the waveguide, so that the overall length of a pair of arms will
be comparable to an integer multiple of half or full wavelengths of
the radiation in the waveguide. This will achieve a resonant
coupling condition. The overall length is the total span of the
antenna formed by arms 72, 74, 76 and 78. That is, for example, the
distance from the outside edge of arm section 80 to the outside
edge of arm section 84 in FIG. 3. This distance is distinct from,
and independent of, the gap length of the structure. The opening or
gap between the arms is comparable to the desired near radiation
field extent, as indicated above.
To most effectively heat the recording medium 40, the heat emission
surface 66 of the optical waveguide 58 is preferably spaced apart
from the medium 40 and, more specifically, spaced apart from the
hard magnetic layer 42, by a distance of about 2 nm to about 50 nm.
It will be appreciated that the separation distance is also
dependent on the fly height required to maintain acceptable reading
and writing (electromagnetic coupling for heating) by the recording
head 30.
The write head of FIG. 2 allows for heating of the recording medium
40 in close proximity to the write pole 36, which applies a
magnetic write field H to the recording medium 40. It also provides
for the ability to align the waveguide 58 with the write pole 36 to
maintain the heating application in the same track of the medium 40
where the writing is taking place. Locating the optical waveguide
58 adjacent to the write pole 36, provides for increased writing
efficiency due to the write field H being applied immediately down
track from where the recording medium 40 has been heated. The hot
spot will ideally raise the temperature of the medium 40 to
approximately 200.degree. C. The recording takes place at the
thermal profile, which can also be called the thermal field or the
thermal distribution, in the medium 40 for which the coercivity is
equal to the applied recording field. Ideally, this thermal profile
should be near the edge of the write pole 36 where the magnetic
field gradients are the largest. This will record the sharpest
transition in the medium 40. The optical waveguide 58 may be
integrally formed with the write pole 36.
In operation, the recording medium 40 passes under the recording
head 30, in the direction indicated by arrow A in FIG. 2. The
source 62 transmits radiant energy via the optical fiber 64 to the
optical waveguide 58. The optical waveguide 58 transmits the
optical energy for heating the storage medium 40. More
specifically, a localized area of the recording layer 42 is heated
to lower the coercivity thereof prior to the write pole 36 applying
a magnetic write field H to the recording medium 40.
Advantageously, this allows for higher coercivity storage media to
be used while limiting the superparamagnetic instabilities that may
occur with such recording media used for high recording
densities.
At a down track location from where the medium 40 is heated, the
magnetic write pole 36 applies a magnetic write field to the medium
40 for storing magnetic data in the recording medium 40. The write
field H is applied while the recording medium 40 remains at a
sufficiently high temperature for lowering the coercivity of the
recording medium 40. This ensures that the write pole 36 can
provide a sufficient or high enough magnetic write field to perform
a write operation on the recording medium 40. As described herein,
the recording head 30 advantageously allows for the point of
writing to be in close proximity to where the recording medium 40
is heated.
FIG. 6 is a side view of a recording head 112 that can be
constructed in accordance with an alternative embodiment of the
invention. In the embodiment of FIG. 6, a semitransparent layer 114
is added within a transparent layer 60.
FIG. 7 is a cross-sectional view of a portion of the waveguide of
FIG. 6. The semitransparent layer 114, in combination with the
surface of the data storage medium creates a resonant cavity 116.
The resonant cavity will enable "recycling" of the electromagnetic
energy, and will thus enhance the throughput efficiency of the
device. The height from the semitransparent layer to the reflecting
surface can be comparable to an integer times half the wavelength
of the radiation.
While particular embodiments of the invention have been described
herein for the purpose of illustrating the invention and not for
the purpose of limiting the same, it will be appreciated by those
of ordinary skill in the art that numerous variations of the
details, materials, and arrangements of parts may be made without
departing from the scope of the invention as defined in the
appended claims.
* * * * *